Saurabh Basu 《physica status solidi b》2001,225(2):379-392

Two‐magnon Raman scattering intensity is obtained for a two‐dimensional (2D) spin‐1/2 antiferromagnet in presence of hopping (off‐diagonal) and on‐site (diagonal) disorder. For hopping disorder it is seen that a minute amount of disorder leads to a substantial broadening of the Raman lineshape. Whereas the amount of on‐site disorder needs to be sufficiently high to obtain any observable broadening in the Raman spectrum. In particular, it is shown that the broadening of the Raman lineshape for the hopping disorder case which arises from an asymmetric energy renormalisation in the magnon spectrum leads to a surprisingly good agreement with the experimentally obtained two‐magnon Raman profile for the copper‐oxide insulators such as La₂CuO₄.  相似文献   

    

S. A. El‐Hakim 《physica status solidi b》2004,241(8):1865-1871

This work deals with the determination of the characteristics of the Coulomb gap (CG) in the density of states (DOS) in the vicinity of the Fermi level, from the analysis of the temperature dependence of dc conductivity in the temperature range (1.5 K–300 K) in germanium, disordered by large fluences of fast reactor neutrons. From application, the percolation theory of conductivity and the variable range hopping (VRH) under the effect of the Coulomb interaction of localized carriers, the localization radius is found to be 49.2 Å. The dielectric constants of the samples are determined. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

M.M. El‐Desoky  I. Kashif 《physica status solidi (a)》2002,194(1):89-105

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S. Ben‐Tabou de‐Leon  B. Laikhtman 《physica status solidi (a)》2002,190(3):689-692

We present the phase diagram of electron–hole plasma in single and coupled quantum wells. In the last case, electrons and holes are spatially separated. In both single and coupled quantum wells there is a Mott transition from electron–hole plasma to exciton gas. Below the Mott transition in a single quantum well there is a crossover to the biexciton gas phase which rules out the Kosterlitz–Thouless transition of excitons. In coupled quantum wells a strong direct repulsion between excitons prevents the biexciton formation. If the separation between electron well and hole well is large enough, the decrease of temperature leads to a transition to a ferromagnetic exciton phase with a spontaneous spin polarization. Further decrease of temperature leads to the Kosterlitz–Thouless transition of the exciton gas.  相似文献   

    

V.V. Nikolaev  M.E. Portnoi 《physica status solidi (a)》2002,190(3):655-660

We study thermodynamic properties of spatially separated electron–hole plasma in double‐layered systems using the Green function formalism. The screening of the Coulomb interaction is considered in the framework of Thomas–Fermi approximation, and a qualitatively new mechanism of screening by indirect excitons is taken into account. The exciton density is shown to decrease sharply with increasing electron–hole separation up to one exciton Bohr radius. The strong mutual enhancement of screening and charge‐separation effects is found.  相似文献   

    

H.Y. Li  S.M. Zhou  J. Du  A. Hu 《physica status solidi (a)》2002,191(2):583-589

The exchange field is found to change as an exponential function of 1/|t₁ — t₂| in two wedged synthetic antiferromagnets FeMn/Co(t₁ = 12.0 nm)/Ru(0.7 nm)/Co(t₂) and FeMn/Co(t₁)/Ru(0.7 nm)/Co(t₂ = 12.0 nm). It has opposite signs and different magnitudes in the two above series. Based on a simple model of magnetization, coherent rotation and magnetically non‐rigid coupling, numerical calculations showed that this asymmetrical and exponential dependence is attributed to a non‐collinear alignment of the magnetizations in the low field range. It is interesting to find that the minor loop has a pronounced asymmetrical shape when the two ferromagnetic layers are close in thickness, hinting the formation of a planar domain wall in the FeMn layer during the magnetization reversal of the ferromagnetic layers.  相似文献   

    

C. Godet 《physica status solidi b》2002,231(2):499-511

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Manisha Pal  K. Hirota  H. Sakata 《physica status solidi (a)》2003,196(2):396-404

DC electrical conductivity of vanadium–tellurite films both as‐deposited by vacuum deposition and annealed at 773 K for 3 h after deposition are investigated in the temperature range of 323–473 K. All as‐deposited films (250–350 nm thickness) show an amorphous structure; the annealed films show some crystalline peaks of TeO₂. The conductivity of the as‐deposited films at 373 K varies from 1.07 × 10^–7 to 3.73 × 10^–15 Scm^–1. With annealing the conductivity increases by a factor of 10 to 10³ due to the presence of some nanocrystals of TeO₂ and also increases with an increase of the V₂O₅ content. The temperature dependence of the conductivity of both as‐deposited and annealed films obeys a non‐adiabatic small polaron hopping conduction mechanism. Seebeck coefficient measurements indicate all the films to be n‐type semiconductors. From absorption edge analysis it is revealed that the optical band gap energy for the films is 2.96 eV and 3.11 eV for as‐deposited films. Urbach tail analysis gives the width of localized states as 0.272 eV and 0.392 eV for two as‐deposited films.  相似文献   

    

L. M. Karlsson  P. Tengvall  I. Lundstrm  H. Arwin 《physica status solidi (a)》2003,197(2):326-330

Backside etching has been utilized to produce gradients of pore size and layer thickness in porous silicon. Human serum albumin (HSA) was adsorbed on such gradients at two different pH values: 4.9, the pI of HSA, and 7.4, the physiological pH. The samples were investigated by scanning electron microscopy, spectroscopic ellipsometry, and autoradiography. The results show that the protein adsorbed displays a gradient along with the pore size and the thickness gradient. The higher the current density used during etching, the more sway‐back shaped curves were seen for the protein adsorption pattern, independent of pH. When 50 mA/cm² current density was used during etching, the quota between the maximal intensity value and the plateau value seen after adsorption of the HSA increased for pH 7.4.  相似文献   

    

A. Szytu&#x;a  A. Jezierski  D. Fus  B. Penc 《physica status solidi (a)》2003,196(1):309-312

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